1. Field of the Invention
This invention relates generally to a mold for transfer molding and more particularly to a mold for transfer molding suitable for packaging, for example, a semiconductor integrated circuit chip by a transfer mold.
2. Description of the Prior Art
As a mold for transfer molding which is used for packaging a semiconductor integrated circuit chip by a transfer mold, there is proposed in the prior art such one as shown in FIG. 1.
In FIG. 1, reference numeral 1 designates a cavity block in which a mold 2 injected with a resin and a gate 3 through which the resin is fed to the mold 2 are formed. Also referring to FIG. 2, a runner 4 which serves as a path through which the resin is flowed is formed on a runner block 5. This runner block 5 is held between a pair of cavity blocks 1, 1 and then they are fixed to a cavity chase 7 which is fixed to a templet 6. A runner block 10 is held by a pair of cavity blocks 9, 9 in each of which a mold 8 injected with the resin is formed and then they are fixed to a cavity chase 12 which is fixed to a templet 11. Then, the cavity block 1 and the cavity block 9 are superposed such that a cavity 13 in which a semiconductor integrated circuit chip is packaged by the resin is formed by the mold 2 formed in the cavity block 1 and the mold 8 formed in the cavity block 9 into which cavity 13 injected is the resin. Further, heaters 14, 15 and temperature detecting elements 16, 17 are respectively provided in the templets 6 and 11, thus a mold for tranfer molding being formed.
By the thus constructed mold for transfer molding, when the semiconductor integrated circuit chip is packaged by, for example, epoxy resin, the mold for transfer molding is at first disposed on a molding press machine 20 through stud members 19 as shown in FIG. 3. Next, as shown in FIG. 4, a semiconductor integrated circuit chip 21 is disposed on a lead frame 22 and an electrode of the semiconductor integrated circuit chip 21 and a lead portion of the lead frame 22 are connected by an Au wire 23. Thereafter, this lead frame 22 is disposed on the cavity block 1 in such a manner that the portion of the lead frame 22 on which the semiconductor integrated circuit chip 21 is disposed is placed at substantially the center portion of the cavity 13. Then, this lead frame 22 is sandwiched with pressure by the cavity blocks 1 and 9. Subsequently, a predetermined current is supplied to the heaters 14 and 15 provided in the templets 6 and 11 to thereby heat the cavity blocks 1 and 9 up to 170.degree. C. Then, an epoxy resin which is pre-heated to 80.degree. C. is injected with pressure through the runner 4 and the gate 3 to the cavity 13 and then cured, whereby to obtain a semiconductor integrated circuit chip 22a which is sealed on the lead frame 22 by the epoxy resin as shown in FIG. 5.
In the prior art mold for transfer molding, however, due to the fact that the templets are not equal in thickness and the mold is thermally distorted by heating the same to a temperature ranging from 160.degree. C. to 180.degree. C., as shown in FIG. 6, the contact surfaces between the cavity blocks 1 and 9 are not satisfactory and hence clearances 23a, 23b, 23c, . . . are formed on the contact surfaces. Then, the resins injected into the cavity 13 is escaped out through these clearances 23a, 23b, 23c, . . . to thereby produce extra resin portions or flashes. There is then a disadvantage that the extra resin portions or flashes must be removed in the later process.
Therefore, as shown in FIG. 7, it is proposed that the cavity block 1 is supported by a strong spring 24 such as a counter-sunk spring and the like so as to remove the influences caused by the uneven thickness of the templets, the heat distortion thereof and so on. In this case, the resin is flowed into the clearances among the cavity chase 7, the runner block 5 and the cavity block 1 and hence cavity block 1 is not moved, producing flashes much more.
For this reason, it has been proposed that as shown in FIG. 8, a thin plate or shim 25 is inserted between the templet 6 and the stud member 19 which corresponds to the place where the flash is produced to thereby satisfactorily contact the cavity blocks 1 and 9 with each other without producing the spacings 23a, 23b, 23c, . . . on the contact surfaces therebetween, thus suppressing the flashes from being produced.
However, the adjustment by the shim 25 takes much time and the re-adjustment thereof is required each time the mold is exchanged and the molding press machine 20 is replaced. Thus, there are disadvantages that the molding takes much time and that the molding pres machine 20 can not be operated effectively.